1. Field of the Invention
The present invention relates to a solenoid-operated valve for opening and closing an intake or exhaust port of an internal combustion engine.
2. Description of the Related Art
There have heretofore been known solenoid-operated valves having a valve body that is operated by solenoids to open and close an intake or exhaust port of an internal combustion engine. Such a solenoid-operated valve has a movable plate connected to the valve body by a transmission valve stem, and first and second solenoids disposed in confronting relation to each other with the movable plate interposed therebetween. The movable plate is attracted by electromagnetic forces that are alternately generated by the first and second solenoids so as to move between the first and second solenoids. When the movable plate is attracted to the first solenoid, the valve body closes the intake or exhaust valve, and when the movable plate is attracted to the second solenoid, the valve body opens the intake or exhaust valve.
If the electric energy alternately supplied to the first and second solenoids is of a constant level, then the electromagnetic force applied to the movable plate by the first solenoid and the electromagnetic force applied to the movable plate by the second solenoid are small when the movable plate is spaced from the first solenoid or the second solenoid, and becomes progressively greater when the movable plate moves closer to the first solenoid or the second solenoid. Therefore, the speed at which the movable plate is displaced increases as the movable plate moves closer to the first solenoid or the second solenoid. When the movable plate is attracted to the first solenoid, since the valve body is displaced at an increased speed, the valve body abruptly closes the intake or exhaust port, tending to produce noise and vibrations when the valve body hits the intake or exhaust port. The movable plate also tends to produce noise and vibrations as it is abruptly attracted to the first solenoid and the second solenoid.
To avoid the above drawbacks, it is customary to supply an increased amount of the electric energy, e.g., a current, to the first and second solenoids when the movable plate is far from the first solenoid or the second solenoid, and supply a reduced amount of the electric energy, e.g., a current, to the first and second solenoids when the movable plate is positioned closely to the first solenoid or the second solenoid. In this manner, when the movable plate is far from the first solenoid or the second solenoid, the speed at which the movable plate is displaced is high, and after the movable plate is positioned closely to the first solenoid or the second solenoid, the speed at which the movable plate is displaced is lowered.
However, controlling only the electric energy supplied to the first and second solenoids is not enough to quickly reduce the speed at which the movable plate is displaced after the movable plate is positioned closely to the first solenoid or the second solenoid.
According to one known solution, a slider is provided to slidingly contact the movable plate or the transmission valve stem when the movable plate is positioned closely to the first solenoid or the second solenoid, thereby exerting an increased sliding resistance to the movable plate or the transmission valve stem. In this fashion, when the movable plate is attracted to the first solenoid or the second solenoid, the movable plate is quickly decelerated to reduce the noise or vibrations produced when the movable plate is attracted to the solenoid. Since the slider is disposed for sliding contact with the movable plate or the transmission valve stem when the movable plate is positioned closely to the first solenoid or the second solenoid, when the movable plate is positioned out of sliding contact with the slider, i.e., positioned away from the solenoid, the movement of the movable plate under the magnetic attractive forces from the solenoid is not impaired by the slider. Consequently, the movable plate can move at sufficient speeds between the first and second solenoids, and can quickly be decelerated after it is positioned closely to the solenoid until attracted thereto.
However, increasing the sliding resistance to the movable plate or the transmission valve stem thereby to reduce the speed at which the movable plate is displaced results in undue wear on the movable plate or the transmission valve stem. After use of the solenoid-operated valve over a long period of time, consequently, the movable plate may not be sufficiently be decelerated.